In the case of electric devices such as an acceleration sensor and pressure sensor arranged in a rotating body such as a tire or rim, it is difficult to supply thereto electric power from a power supply arranged in the vehicle or the like because the devices are arranged in a rotating body. Thus, an internal battery is usually used to operate the electrical circuits of these devices; and when the battery is exhausted, the devices don't operate. Accordingly, the battery must be replaced on a regular basis, thus costing much labor for the replacement. Also, when these electric devices are incorporated into a tire, battery replacement cannot be performed.
In order to solve this problem, there have hitherto been known: a technique which arranges in the surface of a tire or in the interior of a tire, a piezoelectric element which generates electricity when deformation is applied thereto, and supplies to electric devices, electricity generated by the piezoelectric element according to strain which the rotating tire suffers from the ground surface or the like; and a technique by which a plurality of electric power generation coils and magnets are arranged on the same circle around the rotation axis of an axle, and when the plurality of electric power generation coils revolve around the axle together with the wheel and thereby traverse the magnetic field of the magnets, electromotive force is generated (for example, refer to Patent Document 1).
Patent Document 1: Japanese Patent Publication 2004-224069